A “proudly anti-Islam” Australian activist and a YouTuber who sent a rape tweet to a Labour MP have been handed prominent roles at a “family-friendly” Brexit rally due to take place in London on Sunday, the Guardian has learned.

Avi Yemini, who described Islam as a “barbaric ideology” that had taken over England and described Muslim countries as “Islamic sh**holes”, has flown from Australia to cover the event on social media at the invitation of Tommy Robinson, the activist who is organising the event alongside the Ukip leader, Gerard Batten.

Yemini’s attendance is being funded through online donations in partnership with the Canadian far-right website the Rebel Media, which previously employed Robinson.

Ukip has insisted the rally will be a family-friendly demonstration against what it called “the great Brexit betrayal” being pursued by Theresa May’s government. But the Guardian has learned that one of the key confirmed speakers is a man who has accused opponents of “acting like a bunch of [N-word]” and sent a rape tweet to the Labour MP Jess Phillips.

Carl Benjamin, 39, who uses the alias Sargon of Akkad, is a political commentator who has gained more than 860,000 subscribers on YouTube by making videos criticising feminism, Islam and political correctness. He joined Ukip in June as part of the party’s attempt to attract internet-savvy supporters.

The prominent roles of both men at the rally will alarm those inside Ukip who have expressed growing unease about the party’s relationship with Robinson and his associates.

Nigel Farage quit Ukip this week after 25 years, blaming its anti-Muslim “fixation”, while the former deputy chair Suzanne Evans, the former leader Paul Nuttall, and MEPs Patrick O’Flynn, Bill Etheridge and William Dartmouth have also quit following Batten’s decision to appoint Robinson as an adviser.

Robinson, whose real name is Stephen Yaxley-Lennon, has been raising funds for this Sunday’s “Brexit Betrayal” rally by emailing supporters directly, asking for donations towards the £8,000 cost of stage and sound equipment.

Several members of Batten’s inner circle are closely involved with organising the rally, which is due to begin outside the Dorchester hotel and end outside Downing Street. Robinson posted a picture on Instagram from a planning meeting last week which showed the Ukip leader alongside his personal assistant, Liz Phillips, his adviser Lawrence Webb, and the party’s head of communications, Kris Hicks.

A meeting of the ‘Brexit Betrayal’ rally organisers in late November. Photograph: Handout

A senior executive of the Middle East Forum, an influential US thinktank which helped bankroll Robinson’s legal fight and protests, was also at the meeting and has been closely involved in rally preparations, the Guardian has learned.

Lisa Barbounis, the executive liaison officer to the MEF president, Daniel Pipes, is expected to attend the rally. She previously addressed crowds outside the Old Bailey after Robinson’s most recent court appearance.

A Ukip spokesman confirmed Barbounis’ involvement in the meeting and said she was “just recording the meeting to report back to them [the Middle East Forum]”. He said the MEF were “very interested in the topic Tommy Robinson discusses and Brexit and the future prospects of the country”.

However, Pipes denied the forum was “in any way connected” to the Brexit rally. Barbounis was in London “on her own initiative and attended the planning meeting in a personal capacity”, he said.

One senior Ukip insider described the rally as “crazy” and said 200 members had quit the party on Friday night in protest at its association with Robinson. “If it all goes wrong, and I think it will, then Gerard should walk or be pushed,” the insider said.

Benjamin gained notoriety in 2016 when he was accused of instigating a misogynistic trolling campaign against Phillips, the Labour MP for Birmingham Yardley. “I wouldn’t even rape you,” he tweeted at Phillips, reportedly prompting hundreds of threatening tweets against her, including rape and death threats from his followers. He has since been banned from Twitter.

In a livestream recorded in February, Benjamin appeared to lose his temper at commenters. “You are acting like a bunch of [N-word], just so you know. You act like white [N-word],” he said. Benjamin insisted his comments had been taken out of context.

Yemini, who describes himself as “proudly anti-Islam”, gained more than 100,000 followers on Facebook after posting inflammatory videos, before being banned from the social network earlier this week.

The Israeli-born activist says he was a sniper in the Israeli Defence Forces and that he served in the Gaza Strip. He is standing in upcoming elections for the far-right Australian Liberty Alliance party, which has acknowledged donating to Robinson in the past.

His arrival in Britain was welcomed by Daniel Thomas, who was jailed for two years in 2016 for attempted kidnap and is organising the rally with Robinson and Ukip. He posted a picture of Yemini on social media with the message: “My favourite Nazi Jew Avi has arrived #SundayFunDay #TheGreatBetrayal”.

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